Chitin and method for chemically obtaining chitin and/or chitosan

ABSTRACT

The present invention relates to a chitin having a molecular mass of more than 855 kg·mol-1 and to a process for obtaining chitin and/or chitosan by separating cuticles from the soft part of the insect and by a basic treatment of the cuticles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application pursuant to 35 U.S.C. § 371 of International Patent Application PCT/FR2018/053284, filed on Dec. 13, 2018, and published as WO 2019/115969 on Jun. 20, 2019, which claims priority to French Patent Application 1762303, filed on Dec. 15, 2017, all of which are incorporated herein by reference in their entireties for all purposes.

The present invention relates to a chitin, a chitosan and a method for preparing chitin and/or chitosan from insects.

According to the invention, by “chitin” is meant a polymer predominantly composed of glucosamine and N-acetyl glucosamine units, wherein said units can optionally be substituted by amino acids and/or peptides.

By “predominantly composed” is meant that said polymer contains between 55% and 98% by weight, preferably between 75 and 90% by weight, glucosamine and N-acetyl glucosamine units.

Chitin is said to be the second most synthesized polymer in the living world, after cellulose. In fact, chitin is synthesized by a number of species in the living world: it constitutes part of the exoskeleton of crustaceans and insects and the side wall that surrounds and protects fungi. More particularly, in insects, chitin thus constitutes 3 to 60% of their exoskeleton.

By “chitosan” is meant, according to the present invention, the products of deacetylation of chitin. The usual limit between chitosan and chitin is determined by the degree of acetylation: a compound having a degree of acetylation lower than 50% is called chitosan, beyond that a compound having a degree of acetylation higher than 50% is called chitin.

The applications of chitin and/or chitosan are numerous: cosmetic (cosmetic composition), medical and pharmaceutical (pharmaceutical composition, treatment for burns, biomaterials, corneal dressings, surgical threads), dietary and food (human foodstuffs in particular in oenology and animal nutrition, more specifically in aquaculture and aviculture), technical (filtering, texturing, flocculating or adsorbing agent in particular for water filtration and water pollution control), etc. In fact, chitin and/or chitosan are biocompatible, biodegradable and non-toxic materials.

Usually, chitin and chitosan are obtained from different species that synthesize chitin, such as those mentioned above, and in particular from crustaceans or insects.

It is particularly advantageous to obtain chitin and chitosan from insects, as the latter represent an abundant and renewable raw material.

In a number of applications, such as for example cosmetics and pharmacy, it is desired to obtain a chitin and/or a chitosan with a high molecular mass.

By way of example, the use of a chitosan with a high molecular mass makes it possible to maximize the antimicrobial effect and to limit the transepidermal water loss or the irritation of the skin.

In order to obtain a chitosan with a high molecular mass, it is necessary to obtain, first of all, a chitin with a high molecular mass.

In fact, chitosan is obtained by deacetylation of chitin. This step is capable of reducing the molecular mass of the molecule. Thus, the higher the molecular mass of the chitin, the higher the molecular mass of the chitosan obtained from this chitin.

Moreover, the current techniques do not make it possible to increase the molecular mass of the chitin and/or of the chitosan if the chitin and/or the chitosan obtained at the end of a process has (have) a molecular mass insufficient for the intended application.

It is also desired, in particular within the framework of the applications mentioned above, to obtain a chitin and/or a chitosan having a high purity in addition to a high molecular mass.

The invention therefore relates to a chitin, the molecular mass of which is greater than or equal to 855 kg·mol⁻¹.

Advantageously, the molecular mass of the chitin according to the invention is greater than or equal to 900 kg·mol⁻¹, preferably greater than or equal to 950 kg·mol⁻¹, more preferentially greater than or equal to 1000 kg·mol⁻¹.

The molecular mass is determined using the falling ball viscosity measurement.

Preferably, the molecular mass is determined according to a falling ball viscosity measurement method based on the one described in the following publication: “Pacheco et al.; Structural characterization of chitin and chitosan obtained by biological and chemical methods; Biomacromolecules; 12, 3285-3290, 2011”.

More particularly, this method is used and described in Example 1.

Advantageously, the chitin according to the invention contains less than 1.5% by weight amino acids relative to the total dry weight of chitin.

Preferably, the chitin according to the invention contains less than 1% by weight, more preferentially less than 0.9% by weight, still more preferentially less than 0.8% by weight, and still more preferentially less than 0.7% by weight, amino acids relative to the total dry weight of chitin.

Advantageously, the residual amino acids present in the chitin according to the invention are: threonine, glutamic acid, alanine, cysteine, valine, tyrosine, histidine, lysine, tryptophan or a combination of two or more thereof. Preferably, the residual amino acids present in the chitin according to the invention consist of: alanine, cysteine, valine, histidine, lysine, tryptophan or a combination of two or more thereof, preferentially of a combination of all of these amino acids.

The amino acid content of the chitin according to the invention is preferably determined according to the method NF EN ISO 13904 for tryptophan and NF EN ISO 13903 for the other amino acids.

The relative abundance, expressed in percent, can be calculated by relating each amino acid content to the total amino acid content.

Throughout the application, where no date has been specified for a regulation, a standard or a directive, the regulation, standard or directive in force at the filing date is meant.

Advantageously, the chitin according to the invention contains less than 3% by weight ash relative to the total dry weight of chitin.

The chitin according to the invention preferably contains less than 2.75% by weight, more preferentially less than 2.5% by weight, still more preferentially less than 2% by weight, still more preferentially less than 1.8% by weight, ash relative to the total dry weight of chitin.

The method for determining the ash content is well known to a person skilled in the art. Preferably, this content is determined according to the NF V18-101 standard.

Advantageously, the chitin according to the invention contains less than 1% by weight, preferably less than 0.75% by weight, more preferentially less than 0.5% by weight, still more preferentially less than 0.2% by weight, lipids relative to the total dry weight of chitin.

Still more preferentially, the chitin according to the invention does not contain any lipids.

The methods for determining the lipid or fat content are well known to a person skilled in the art. By way of example and preferably, the determination of this content will be carried out following the method from EC 152/2009 regulation.

The chitin according to the invention thus has low amino acid, lipid and ash contents, and therefore has a high purity.

In fact, within the framework of the present application, in order to measure the purity, the known impurity contents, namely amino acids, lipids and ash, are subtracted from the absolute purity value (100%) in order to obtain the value of the estimated purity by difference. Thus, for example, a sample which contains 30% amino acids, 10% lipids and 1% ash is consequently attributed a purity by difference of 100−30−10−1=59%.

Thus, the chitin according to the invention advantageously has a purity by difference greater than or equal to 95%.

Preferably, the chitin according to the invention has a purity by difference greater than or equal to 96%, preferably greater than or equal to 97%.

Preferably, the chitin according to the invention is an isolated chitin.

By “isolated” chitin is meant a chitin which has been isolated or extracted from its natural environment.

More particularly, within the framework of the present application, the chitin is isolated or extracted from insects, more specifically from insect cuticles.

The invention relates moreover to a chitosan, the molecular mass of which is greater than or equal to 250 kg·mol⁻¹.

Advantageously, the molecular mass of the chitosan according to the invention is greater than or equal to 300 kg·mol⁻¹, preferably greater than or equal to 325 kg·mol⁻¹, more preferentially greater than or equal to 350 kg·mol⁻¹.

The molecular mass is determined in the same manner as indicated above for the chitin according to the invention.

The chitosan according to the invention also has a high purity.

In fact, the chitosan according to the invention advantageously has a purity by difference greater than or equal to 95%.

Preferably, the chitosan according to the invention has a purity by difference greater than or equal to 96%, preferably greater than or equal to 97%.

The purity by difference, the amino acid content, the ash content, and the lipid content of the chitosan according to the invention are measured in the same manner as indicated above for the chitin.

Advantageously, the chitosan according to the invention contains less than 1.5% by weight amino acids relative to the total dry weight of chitosan.

Preferably, the chitosan according to the invention contains less than 1% by weight, more preferentially less than 0.8% by weight, still more preferentially less than 0.5% by weight, still more preferentially less than 0.4% by weight, amino acids relative to the total dry weight of chitosan.

Advantageously, the residual amino acids present in the chitosan according to the invention are: threonine, lysine and/or tryptophan.

Advantageously, the chitosan according to the invention contains less than 3% by weight ash relative to the total dry weight of chitosan.

The chitosan according to the invention preferably contains less than 2.75% by weight, more preferentially less than 2.5% by weight, ash relative to the total dry weight of chitosan.

Advantageously, the chitosan according to the invention contains less than 1% by weight, preferably less than 0.75% by weight, more preferentially less than 0.5% by weight, lipids relative to the total dry weight of chitosan.

Preferably, the chitosan according to the invention is an isolated chitosan.

By “isolated” chitosan is meant a chitosan which has been obtained from a chitin isolated or extracted from its natural environment.

More particularly, within the framework of the present application, the chitosan is obtained from a chitin isolated or extracted from insects, more specifically from insect cuticles.

The invention also relates to a method for obtaining chitin and/or chitosan, from insects, comprising the following steps:

-   -   separation of the cuticles from the soft part of the insects,         then     -   basic treatment of the cuticles.

The method for obtaining chitin and/or chitosan according to the invention makes it possible to obtain a chitin and/or a chitosan with a high molecular mass. Moreover, the chitin and/or the chitosan also have a high purity, e.g. a high purity by difference.

By “insects” is meant insects at any stage of development, such as an adult stage, a larval stage or a nymph stage (intermediate stage). Advantageously, the insects used in the method according to the invention are at a larval stage if the insects are holometabolous, at a nymph stage (intermediate stage) if the insects are heterometabolous, or at an adult stage where appropriate.

The insects used in the method according to the invention can be edible.

Advantageously, the insects preferred for use in the method according to the invention are for example coleopterans (beetle), dipterans, lepidopterans (such as for example Galleria mellonella), isopterans, orthopterans, hymenopterans, blattopterans, hemipterans, heteropterans, ephemeropterans and mecopterans, preferably coleopterans, dipterans, orthopterans, lepidopterans or mixtures thereof, still more preferentially coleopterans.

The coleopterans preferentially used in the method according to the invention belong to the families Tenebrionidae, Melolonthidae, Dermestidae, Coccinellidae, Cerambycidae, Carabidae, Buprestidae, Cetoniidae, Dryophthoridae, or mixtures thereof.

More preferentially, they are the following coleopterans: Tenebrio molitor, Alphitobius diaperinus, Zophobas mono, Tenebrio obscurus, Tribolium castaneum, Pachnoda marginata and Rhynchophorus ferrugineus, or mixtures thereof. Still more preferentially, they are Tenebrio molitor.

The method for obtaining chitin and/or chitosan according to the invention comprises a step of separating the cuticles from the soft part of the insects.

The cuticle is the external layer (or exoskeleton) secreted by the epidermis of insects. In general it is formed of three layers: the epicuticle, the exocuticle and the endocuticle.

By “soft part” is meant the flesh (comprising in particular the muscles and the viscera) and the juice (comprising in particular body fluids, water and haemolymph) of insects. In particular, the soft part does not consist of the juice of the insects.

The separation of the cuticles from the soft part of the insects can be performed using any suitable type of separator.

According to a first embodiment, the separation of the cuticles from the soft part is carried out using a belt separator.

According to a second embodiment, the separation of the cuticles from the soft part is carried out using a filter press.

This step of separating the cuticles from the soft part of the insects is described more fully in step 2 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

This separation of the cuticles from the soft part of the insect makes it possible in particular to separate the chitin from the soft part. In fact, the cuticles obtained at the end of this separation step have a high chitin content of the order of 10 to 30% by weight relative to the total weight of cuticles, as indicated hereafter.

In particular, the step of separating the cuticles from the soft part is performed without any prior step of grinding the insects, in particular in the form of particles, having been performed.

The method for obtaining chitin and/or chitosan according to the invention advantageously comprises a killing step prior to the step of separating the cuticles from the soft part.

This killing step is described more fully in step 1 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

Advantageously, following killing step 1, the insects are directly used to carry out step 2 of separating the cuticles from the soft part of the insects, i.e. the insects are not subjected to any treatment, such as grinding, freezing or dehydration, between step 1 and step 2.

The method for obtaining chitin and/or chitosan according to the invention comprises a step of basic treatment of the cuticles, following the step of separating the cuticles from the soft part of the insects.

Advantageously, the basic treatment is carried out using a strong base.

Advantageously, the strong base is chosen from sodium hydroxide or caustic soda, potassium hydroxide, and ammonium hydroxide. Preferably, the strong base is sodium hydroxide.

Preferably, the base used for the basic treatment is in the form of an aqueous basic solution.

In this case, the molar concentration of the base in aqueous solution is advantageously comprised between 0.1 and 5 mol·L⁻¹, preferably comprised between 0.5 and 2 mol·L⁻¹, still more preferentially equal to 1 mol·L⁻¹ (for example molar caustic soda).

It will be noted that, within the framework of the present application, and unless stipulated otherwise, the ranges of values indicated are understood to be inclusive.

Preferably, the concentration of the base is adjusted so as to obtain a ratio of base by dry weight in g:cuticles by dry weight in g:water by weight in g comprised between 0.4:0.45:10 and 1.4:0.45:30, more preferentially 0.4:0.45:10 and 1.2:0.45:30, still more preferentially approximately 0.9:0.45:22. The most preferred values are in particular those to be used when sodium hydroxide is used.

This step of basic treatment of the cuticles is described more fully in step 3 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

Advantageously, the step of basic treatment of the cuticles is followed by a step of recovering the chitin.

This step of recovering the chitin is described more fully in step 4 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

Optionally, the method for obtaining chitin and/or chitosan according to the invention moreover comprises a step of washing the chitin.

This optional step of washing the chitin is described more fully in step 5 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

Optionally, the method for obtaining chitin and/or chitosan according to the invention moreover comprises a step of drying the chitin.

This optional step of drying the chitin is described more fully in step 6 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

As the chitin can be sold in the form of powder, the method for obtaining chitin and/or chitosan according to the invention can optionally comprise a step of grinding the chitin.

This optional step of grinding the chitin is described more fully in step 7 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

The grinding step can also be performed in order to promote the deacetylation reaction, which makes it possible to prepare chitosan from chitin.

The deacetylation step, which is intended to convert the chitin to chitosan, is therefore only carried out if the desired product is chitosan.

This step of deacetylation of the chitin is described more fully in step 8 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

Advantageously, the step of deacetylation of the chitin is followed by a step of recovering the chitosan.

This step of recovering the chitosan is described more fully in step 9 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

Optionally, the method for obtaining chitin and/or chitosan according to the invention moreover comprises a step of washing the chitosan.

This optional step of washing the chitosan is described more fully in step 10 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

Optionally, the method for obtaining chitin and/or chitosan according to the invention moreover comprises a step of drying the chitosan.

This optional step of drying the chitosan is described more fully in step 11 of the detailed method for obtaining chitin and/or chitosan according to the invention hereafter.

Preferably, the methods for obtaining chitin and/or chitosan according to the invention do not comprise a step carried out at a pH lower than 6.

It will be noted that steps 5 to 7, 10 and 11 mentioned above, and described more fully in the detailed method for obtaining chitin and/or chitosan according to the invention hereafter, are optional. However, the method for obtaining chitin and/or chitosan according to the invention advantageously comprises one or more of these steps, preferably all of these steps.

It will additionally be noted that the features of steps 1 to 11 of the detailed method for obtaining chitin and/or chitosan according to the invention, which are described hereafter, are not limited to a use in said detailed method, but apply to all of the embodiments of the method for obtaining chitin and/or chitosan according to the invention described in the present application, independently of the number of steps provided in these embodiments.

These features also apply to a particular method for obtaining chitin and to a particular method for obtaining chitosan according to the invention, described hereafter.

The invention is therefore aimed more particularly at a particular method for obtaining chitin, from insects, comprising the following steps:

-   -   killing of the insects,     -   separation of the cuticles from the soft part of the insects,     -   basic treatment of the cuticles,     -   recovery of the chitin.

This method therefore comprises steps 1 to 4 of the detailed method for obtaining chitin and/or chitosan hereafter and advantageously one or more of the optional steps 5 to 7 of this detailed method.

The invention also relates to the chitin that can be obtained using the method for obtaining chitin and/or chitosan according to the invention, or using the particular method for obtaining chitin according to the invention.

The invention is therefore also aimed at a particular method for obtaining chitosan, from insects, comprising the following steps:

-   -   killing of the insects,     -   separation of the cuticles from the soft part of the insects,     -   basic treatment of the cuticles,     -   recovery of the chitin,     -   deacetylation of the chitin, and     -   recovery of the chitosan.

This method therefore comprises steps 1 to 4, 8 and 9 of the detailed method for obtaining chitin and/or chitosan hereafter and advantageously one or more of the optional steps 5 to 7, 10 and 11 of this detailed method.

The invention also relates to the chitosan that can be obtained using the method for obtaining chitin and/or chitosan according to the invention, or using the particular method for obtaining chitosan according to the invention.

The chitin and/or the chitosan according to the invention and the chitin and/or the chitosan that can be obtained using a method according to the invention can advantageously be used in various applications:

-   -   in cosmetic, pharmaceutical, nutraceutical or dietary         compositions,     -   as biomaterials for treating burns, as a second skin, in order         to make corneal dressings or surgical threads,     -   as filtering, texturing, flocculating and/or adsorbing agent in         particular for water filtration and water pollution control.

Detailed Method for Obtaining Chitin and/or Chitosan According to the Invention

-   -   Step 1: Killing of the insects

This killing step 1 can advantageously be performed by thermal shock, such as by scalding or by blanching. This step 1 makes it possible to kill the insects while lowering the microbial load (reducing the risk of alteration and health risk) and inactivating the internal enzymes of the insects that can trigger autolysis, and thus a rapid browning of them.

For the scalding, the insects, preferably the larvae, are thus scalded in water for 2 to 20 minutes, preferentially 5 to 15 minutes. Preferably, the water is at a temperature comprised between 87 and 100° C., preferentially 92 and 95° C.

The quantity of water introduced during the scalding is determined as follows: the ratio of the volume of water in ml to the weight in g of insect is preferably comprised between 0.3 and 10, more preferentially between 0.5 and 5, still more preferentially between 0.7 and 3, still more preferentially of the order of 1.

For the blanching, the insects, preferably the larvae, are blanched in water or in steam (steam nozzles or bed) at a temperature comprised between 80 and 105° C., preferably between 87 and 105° C., more preferentially between 95 and 100° C., still more preferentially 98° C. or even in water at a temperature comprised between 90 and 100° C., preferentially between 92 and 95° C. (through spray nozzles) or in a mixed mode (water+steam) at a temperature comprised between 80 and 130° C., preferably between 90 and 120° C., more preferentially between 95 and 105° C., still more preferentially 98° C. If the insects are blanched only in steam, the blanching is advantageously carried out in forced steaming blanching machines. The residence time in the blanching chamber is comprised between 5 seconds and 15 minutes, preferentially between 1 and 7 minutes.

Advantageously, following killing step 1, the insects are directly used to carry out step 2 of separating the cuticles from the soft part of the insects, i.e. the insects are not subjected to any treatment, such as grinding, freezing or dehydration, between step 1 and step 2.

According to a preferred embodiment, the insects are coleopterans and in particular Tenebrio molitor.

-   -   Step 2: Separation of the cuticles from the soft part of the         insects

The objective of step 2 is to separate the cuticles from the soft part of the insects.

The separation of the cuticles from the soft part of the insects can be performed using any suitable type of separator.

According to a first embodiment, the separation of the cuticles from the soft part is carried out using a belt separator.

By “belt separator” is meant a device that makes it possible to separate the solid part from the soft part of a product, and which comprises a squeezing belt (or belt press) and a perforated drum.

By way of example, a belt separator can comprise a squeezing belt and a perforated drum, wherein the squeezing belt surrounds at least part of the perforated drum.

The squeezing belt allows the insects to be conveyed to and applied against the perforated drum so as to make the soft part of the insects pass, by pressure, through the perforations of the drum, while the solid part of the insects (cuticles) remains outside the drum.

The cuticles can then be recovered using a scraper blade.

By way of example, there may be mentioned the belt separators from the Baader company, such as the belt separators 601 to 607 (“soft separator 601 to 607”), or else the SEPAmatic® belt separators from BFD Corporation (range 410 to 4000V).

Advantageously, the diameter of the perforations of the drum is comprised between 0.5 and 3 mm, preferably between 1 and 2 mm.

With regard to the pressure, a person skilled in the art is capable of determining the pressure to be exerted to make it possible to separate the cuticles from the soft part of the insects.

According to a second embodiment, the separation of the cuticles from the soft part is carried out using a filter press.

A filter press is composed of filter cloths, and allows a separation according to the principle of pressure filtration.

Advantageously, the filter press used in the method for obtaining chitin and/or chitosan according to the invention is a belt filter press.

A belt filter press comprises two perforated squeezing belts (also called “filter cloths”). The insects are placed between the two perforated squeezing belts so as to make the soft part of the insects pass, by pressure, through the perforations of the squeezing belts, while the solid part of the insects remains between the two perforated squeezing belts.

A person skilled in the art is capable of determining the diameter of the perforations of the squeezing belts as well as the pressure to be exerted to make it possible to separate the cuticles from the soft part of the insects.

By way of example, there may be mentioned the belt filter press (or “belt press”) from the Flottweg company, or also the belt filter presses from the ATR Creations company.

This step of separating the insects differs from conventional pressing that can be carried out for example with a single or twin screw press in that it makes it possible to (cleanly) separate the soft part and the cuticles of the insects and not to separate a juice from a solid fraction.

Advantageously, the separation of the cuticles from the soft part of the insects is performed using a belt separator.

The cuticles obtained in step 2 contain between 10 and 30%, preferably between 15 and 25%, by weight chitin, relative to the total dry weight of cuticles.

The chitin content is determined by extraction thereof. By way of example, a method for determining the chitin content that can be used is the AOAC 991.43 method.

According to a preferred embodiment, the separation of the cuticles from the soft part of coleopterans and in particular of Tenebrio molitor is performed using a belt separator.

-   -   Step 3: Basic treatment of the cuticles

In step 3, the cuticles recovered at the end of step 2 are subjected to a basic treatment, i.e. they are brought into contact with a base (or basic agent).

Advantageously, the basic treatment is carried out using a strong base.

Advantageously, the strong base is chosen from sodium hydroxide or caustic soda, potassium hydroxide, and ammonium hydroxide. Preferably, the strong base is sodium or potassium hydroxide, more preferentially sodium hydroxide.

Preferably, the base used for the basic treatment is in the form of an aqueous basic solution.

In this case, the molar concentration of the base in aqueous solution is advantageously comprised between 0.1 and 5 mol·L⁻¹, preferably comprised between 0.5 and 2 mol·L⁻¹, still more preferentially equal to 1 mol·L⁻¹ (for example molar caustic soda).

Preferably, the concentration of the base is adjusted so as to obtain a ratio of base by dry weight in g:cuticles by dry weight in g:water by weight in g comprised between 0.4:0.45:10 and 1.4:0.45:30, more preferentially 0.4:0.45:10 and 1.2:0.45:30, still more preferentially approximately 0.8:0.45:20. The most preferred values are in particular those to be used when sodium hydroxide is used.

The basic treatment is advantageously carried out for a duration comprised between 5 and 60 hours, preferably for a duration comprised between 10 and 60 hours, more preferentially between 15 and 55 hours.

The duration of the basic treatment can advantageously be adapted according to the properties of the chitin that it is desired to obtain, such as its whiteness.

For example, in the case where it is not particularly desired to obtain a white-coloured chitin, the duration of the basic treatment can be less than 30 hours, such as for example approximately 20 hours.

On the other hand, in the case where it is desired to obtain a white-coloured chitin, and in particular if the insects are coleopterans and orthopterans, the duration of the basic treatment will advantageously be at least 30 hours, preferably at least 40 hours, such as for example approximately 48 hours.

Advantageously, the basic treatment is carried out at a temperature comprised between 60 and 100° C., preferably comprised between 80 and 100° C., more preferentially approximately 90° C.

Therefore, the reaction medium can be heated, for example using an oil bath, a heat exchanger or a double-envelope heating system, so as to reach the desired temperature.

The step of basic treatment is advantageously carried out under stirring.

-   -   Step 4: Recovery of the chitin

Step 4 of recovering the chitin, from the reaction medium obtained at the end of step 3, can be carried out using any suitable recovery method. These methods are known to a person skilled in the art.

By way of example, there may be mentioned filtration, centrifugation and decantation.

Advantageously, the recovery of the chitin is carried out by filtration.

-   -   (Optional) step 5: Washing of the chitin

The chitin recovered at the end of step 4 is then optionally washed.

Step 5 of washing the chitin is advantageously carried out using tap water or distilled water, preferably using tap water. Preferably, this water has a temperature comprised between 15 and 60° C.

Preferably, the washing is carried out until neutralization of the pH.

-   -   (Optional) step 6: Drying of the chitin

The chitin is then optionally dried.

Preferably, the drying step is carried out at a temperature comprised between 40 and 105° C., preferably at approximately 60° C.

The drying step is carried out for a duration comprised between 10 and 80 hours, preferably for approximately 24 hours.

Advantageously, the drying is carried out using a drying oven, such as the FED 115 or FP53 model from the Binder® company.

In order to prepare chitosan from chitin, the following steps can be carried out in addition:

-   -   (Optional) step 7: Grinding of the chitin

The chitin obtained at the end of step 4, 5 or 6 is then optionally ground, for example in an ultra centrifugal grinder with a sieve.

The production of chitosan from chitin, by deacetylation reaction, largely depends on the size of the chitin particles. Thus, a very fine grinding of the chitin before deacetylation makes it possible to significantly increase the yields and the speed of the deacetylation reaction, as is illustrated in Table 1 below:

TABLE 1 Efficiency of the deacetylation depending on the prior grinding of the chitin Grinding Grinding Grinding Grinding 30 s 45 s 60 s 120 s 50% of the <174 μm <117 μm  <95 μm  <67 μm particles 90% of the <310 μm <244 μm <157 μm <159 μm particles DA* 99% 90% 85% 80% *Measurement of the Degree of Acetylation DA

The conditions of the deacetylation performed in the test reported in Table 1 are as follows: 4 hours of reaction, 100° C., NaOH in aqueous solution at 30% by volume, in a ratio of estimated chitin:NaOH solution equal to 1:20.

As a result, the chitin is preferentially ground to a particle size smaller than 300 μm, such as a size smaller than 260, or smaller than 200 μm, or also smaller than 160 μm.

-   -   Step 8: Deacetylation of the chitin

This step is only carried out in the case where it is desired to obtain chitosan.

The chitin is then placed in a reactor, where a base is added.

Advantageously, the deacetylation of the chitin is carried out using a strong base.

Advantageously, the strong base is chosen from sodium hydroxide or caustic soda, potassium hydroxide, and ammonium hydroxide. Preferably, the strong base is sodium hydroxide.

Preferably, the base used for the basic treatment is in the form of an aqueous basic solution, preferably a concentrated aqueous basic solution.

In this case, the molar concentration of the base in aqueous solution is advantageously comprised between 4 and 25 mol·L⁻¹, preferably comprised between 6 and 22 mol·L⁻¹, more preferentially comprised between 8 and 19 mol·L⁻¹, still more preferentially comprised between 10 and 19 mol·L⁻¹, still more preferentially comprised between 12.5 and 19 mol·L⁻¹.

Preferably, the concentration of the base is adjusted so as to obtain a ratio of base by dry weight in g:chitin by dry weight in g:to water by weight in g comprised between 18:1:35 and 55:1:55, such as for example comprised between 18:1:35 and 30:1:55, or approximately 24:1:45, more preferentially approximately 38:1:50. The most preferred values are in particular those to be used when sodium hydroxide is used.

Preferably, the deacetylation is carried out for 1 to 24 hours and preferentially 2 to 18 hours.

Advantageously, this deacetylation is carried out in two runs, with an intermediate step of neutralizing the pH. For example, the deacetylation can be carried out in two runs of two hours, i.e. for 4 hours, with an intermediate step of neutralizing the pH in between.

The deacetylation temperature is advantageously between 80 and 150° C., preferably between 90 and 120° C. and more preferentially at 100° C.

-   -   Step 9: Recovery of the chitosan

Step 9 of recovering the chitosan, from the reaction medium obtained at the end of step 8, can be carried out using any suitable recovery method. These methods are known to a person skilled in the art.

By way of example, there may be mentioned filtration, centrifugation and decantation.

Advantageously, the recovery of the chitosan is carried out by filtration.

In the case where step 7 of grinding the chitin is carried out, the chitosan recovered is in the form of powder.

The chitosan can then be subjected to any operation known to a person skilled in the art that makes it possible to functionalize it, in particular by the addition of radicals (carboxylation, hydroxylation, etc.).

-   -   (Optional) step 10: Washing

The chitosan recovered at the end of step 9 is then optionally washed.

Step 10 of washing the chitosan is advantageously carried out using tap water. Preferably, this water has a temperature comprised between 15 and 60° C.

Preferably, the washing is carried out until neutralization of the pH.

-   -   (Optional) step 11: Drying

The chitosan, which can be in the form of powder, is then optionally dried between 30 and 80° C., advantageously between 50 and 70° C., preferably at approximately 60° C., in order to obtain chitosan or a chitosan powder having a dry matter content greater than 85%, more particularly greater than 90%.

The drying step is carried out for a duration comprised between 10 and 80 hours, preferably for approximately 24 hours.

Advantageously, the drying is carried out using a drying oven, such as the FED 115 or FP 53 model from the Binder® company.

The invention will be better understood in the light of the following examples, which are given by way of illustration.

Example 1: Method for Obtaining Chitin According to the Invention

I. Obtention Method

Larvae of Tenebrio molitor were used. On receipt of the larvae, the latter can be stored at 4° C. for 0 to 15 days in their rearing trays before being killed, without major degradation. The weight of the larvae (age) used is variable and as a result their composition can vary, as is illustrated in Table 2 below:

TABLE 2 Biochemical composition of the larvae of Tenebrio molitor according to their weight. Biomass (insects) mg 23 35 58 80 108 154 Dry matter %* 34 34 34.2 37.9 39.6 39.5 Ash %* 1.59 1.52 1.6 1.75 1.67 1.43 Crude proteins %* 22.6 22.2 22 23.2 23.1 23.2 Lipids %* 6.62 6.88 7.98 10.3 10.9 11.7 *The % are expressed in dry weight relative to the wet weight of larvae.

-   -   Step 1: Killing of the insects

The living larvae (+4° C. to +25° C.) are conveyed, in a layer with a thickness comprised between 2 and 10 cm, on a perforated conveyor belt (1 mm) to a blanching chamber. The insects are thus blanched in steam (steam nozzles or bed) at 98° C. under forced ventilation or else in water at 92-95° C. (spray nozzles) or in a mixed mode (water+steam). The residence time in the blanching chamber is comprised between 5 seconds and 15 minutes, ideally 5 minutes.

The temperature of the larvae after blanching is comprised between 75° C. and 98° C.

-   -   Step 2: Separation of the soft part from the cuticles of the         insects

The larvae, once blanched, are conveyed to the feed hopper of a belt separator, in order to separate the cuticles from the soft part of the larvae.

Advantageously, the separation is performed immediately after killing, such that the larvae do not have time to cool to ambient temperature.

The belt separator used is a belt separator 601 from the Baader company.

The diameter of the perforations of the drum is 1.3 mm.

The soft part of the insects is recovered in a tank.

The cuticles are recovered using a scraper blade.

The percentage of dry matter in the cuticles is approximately 45%.

The moisture content of the cuticles is therefore approximately 55%.

-   -   Step 3: Basic treatment of the cuticles

90.02±0.02 g wet cuticles obtained in step 2 (Dry Matter=40.1±0.1%) and 1.80±0.02 L aqueous sodium hydroxide solution with a concentration equal to 1 mol·L⁻¹ are placed in a 2-L three-neck flask equipped with a condenser and a mechanical stirrer (Heidolph® RZR1). The medium is heated with an oil bath to a temperature of 90±2° C. for 48 hours. Throughout the reaction, the reaction medium is subjected to a stirring of 280 rpm.

The ratio of base by dry weight in g:cuticles by dry weight in g:water by weight in g is approximately equal to 0.9:0.45:22.

-   -   Step 4: Recovery of the chitin

The reaction medium obtained at the end of step 3 is then filtered (SEFAR MEDIFAB® 03-60/42 filter) so as to recover the chitin.

-   -   (Optional) step 5: Washing of the chitin

The chitin recovered at the end of step 4 is then rinsed with tepid tap water until neutralization of the pH.

-   -   (Optional) step 6: Drying of the chitin

The chitin is then dried for 24 hours, at 60° C., in a drying oven (Binder®, FP53 model).

6.3±0.2 g chitin is thus obtained.

II. Analysis Methods

Measurement of the Dry Matter and of the Moisture Content

The percentage of dry matter and the moisture content are calculated as follows.

2 g chitin are weighed into cups, introduced into a drying oven (Binder®, FED 115 model) and dried at 105° C. for 24 h (or until completely dry).

The percentage of dry matter is obtained by making the ratio of the dry mass of chitin after drying to the mass of chitin before drying.

The moisture content is obtained by subtracting the percentage of dry matter from the value of 100%.

This measurement method can also be used to measure the percentage of dry matter and the moisture content of the cuticles.

Measurement of the Ash Content

The ash content was determined according to the method from NF V18-101 standard.

Measurement of the Crude Protein Content

The protein content is obtained using the Dumas method, with the conversion coefficient of 6.25, adapted from the NF EN ISO 16634-1 standard.

Measurement of the Lipid or Fat Content

The lipid content is obtained using a method adapted from the EC 152/2009 regulation-B Method-SN.

Amino Acid Content and Relative Abundance

The amino acid content of the chitin according to the invention is preferably determined according to the NF EN ISO 13904 method or a method adapted from the EC 152/2009 regulation of 27-01-2009-SN (these two methods being equivalent) for tryptophan, and according to the NF EN ISO 13903 method or a method from the EC 152/2009 regulation of 27-01-2009-SN for the other amino acids (these two methods being equivalent).

The relative abundance was calculated by relating each amino acid content to the total amino acid content.

Total Amino Acid Content

The total amino acid content was determined by adding up the individual values obtained for each amino acid, including tryptophan.

Purity by Difference

For this measurement, the known impurity contents (amino acids, lipids and ash) were subtracted from the absolute purity value (100%) in order to obtain the value of the estimated purity by difference. Thus, for example, a sample which contains 30% amino acids, 10% lipids and 1% ash is consequently attributed a purity by difference of 100−30−10−1=59%.

Molecular Mass of the Chitin

The method for determining the molecular mass of the chitin is based on viscosity measurements of diluted solutions of chitin. The dilutions are carried out in dimethylacetamide containing 5% lithium chloride (DMAc-LiCl 5%). In fact, the polymers in solution increase the viscosity of a solvent. The viscosity of the polymer in solution depends on its concentration and its molecular mass. The relationship is defined by the Mark-Houwink-Sakurada equation: [η]=KM ^(α)

with [η]: the intrinsic viscosity, M: the molecular mass, K and a specific constants of a solvent/polymer system at a given temperature.

The values for chitin dissolved in the solvent DMAc-LiCl 5% at 25° C. are: K=0.24 mL·g⁻¹ and α=0.69 (Pacheco et al.; 2011).

The intrinsic viscosity corresponds to the specific viscosity when the concentration of the polymer tends towards zero.

$\lbrack\eta\rbrack = {\lim\limits_{c\rightarrow 0}\left( \frac{\eta\;{sp}}{c} \right)}$

In order to measure the specific viscosity of the chitin, five solutions with weak concentrations are prepared in DMAc-LiCl 5%. The flow times of the solvent alone (to) and of the solutions (t) with different concentrations are measured using a falling ball micro viscometer in order to calculate the relative viscosity (η_(r)). From the relative viscosity OM, it is necessary to calculate the specific (η_(sp)), reduced (η_(red)) and inherent (η_(inh)) viscosities of each concentration of chitin.

${\eta_{sp} = {\eta_{r} - 1}};{\eta_{red} = \frac{\eta\;{sp}}{c}};{\eta_{inh} = \frac{\ln\left( {\eta\; r} \right)}{c}}$

The intrinsic viscosity is then calculated by plotting the curves “concentration vs. reduced viscosity” (positive slope) and “concentration vs. inherent viscosity” (negative slope). Each of these curves is extrapolated from zero concentration. The y-intercept corresponds to the intrinsic viscosity. Similar results are expected from the two curves. Finally, in order to determine the molecular mass of the chitin, the Mark-Houwink-Sakurada equation is applied.

III. Results

The properties of the chitin obtained at the end of step 6 are given in Table 3 below.

TABLE 3 Properties of the chitin obtained in Example 1 Ash (g/100 g DM*) 1.71 +/− 0.11 Fats (g/100 g DM*)   0 +/− 0.00 Total aa** content (g/100 g DM*) 0.68 +/− 0.03 Purity by difference (%) 97.61 +/− 0.14  Molecular mass (kg · mol⁻¹) 1015.5 +/− 98.29  *DM: dry matter **aa: amino acids

The relative abundance of amino acids in the chitin obtained is given in Table 4 below. It is expressed in %.

TABLE 4 Relative abundance of amino acids in the chitin obtained in Example 1 Threonine (Thr) 0.00 Serine (Ser) 0.00 Proline (Pro) 0.00 Glycine (Gly) 0.00 Glutamic acid (Glu) 0.00 Alanine (Ala) 12.48 Cysteine (Cys) 5.87 Valine (Val) 8.07 Methionine (Met) 0.00 Isoleucine (Ile) 0.00 Aspartic acid (Asp) 0.00 Leucine (Leu) 0.00 Tyrosine (Tyr) 0.00 Phenylalanine (Phe) 0.00 Histidine (His) 44.77 Lysine (Lys) 28.62 Arginine (Arg) 0.00 Tryptophan (Trp) 0.19 Total 100.00

5 amino acids appear to be particularly resistant to the method, namely alanine, cysteine, valine, histidine and lysine. Histidine, lysine and alanine are the 3 most resistant amino acids. In fact they represent more than 85% of the residual amino acids.

Example 2: Method for Obtaining Chitosan According to the Invention

In order to prepare chitosan, the chitin resulting from step 4, 5 or 6 of Example 1 is used.

-   -   (Optional) step 7: Grinding of the chitin The chitin was ground         in an ultra centrifugal grinder with a sieve to a size of 250         μm.     -   Step 8: Deacetylation of the chitin

The chitin is then placed in a reactor, where a concentrated caustic soda solution is added. The sodium hydroxide in aqueous solution at a level of 50% (i.e. a concentration of sodium hydroxide in aqueous solution of 12.5 mol/L) is added in a ratio of weight in g ground chitin/volume in mL sodium hydroxide in aqueous solution equal to 1:50. The tank is then heated to a temperature of 100° C. The deacetylation reaction is carried out for 2 hours twice, with an intermediate step of neutralization of the pH.

-   -   Step 9: Recovery of the chitosan

The reaction medium obtained at the end of step 8 is then filtered (SEFAR MEDIFAB® 03-60/42 filter) so as to recover the chitosan.

-   -   (Optional) step 10: Washing

The chitosan recovered at the end of step 9 is then rinsed with tepid tap water until neutralization of the pH.

Powdered chitosan is thus obtained.

The molecular mass of the chitosan obtained is equal to 350+/−26 kg·mol⁻¹.

The purity by difference of the chitosan obtained is greater than 97%.

-   -   (Optional) step 11: Drying

The chitosan powder is then dried at 60° C. in order to obtain a powder having a dry matter content greater than 85%.

Example 3: Comparative Method for Obtaining Chitin

This comparative method does not comprise a step of separating the soft part from the cuticles of the insects (step 2 of the method according to the invention), but does comprise a step of grinding then pressing the insects (step 2 of the comparative method).

I. Materials and Methods

-   -   Step 1: Killing of the insects         This step is identical to the one in Example 1.     -   Step 2: Grinding then pressing of the insects

Following step 1, 600 g larvae are introduced into a beaker containing 450 mL water, and mixed using a Thermomix® mixer, at maximum speed for 30 seconds. The thus-obtained liquid is pressed with a twin screw press of the Angel type under the following conditions:

Speed=82 rpm;

W (energy)=3 HP (horsepower) i.e. 2.68×10⁶ J;

Porosity (approximate)=0.5 mm in the first part and 0.2 mm in the last part.

A press juice and a press cake of 133.1±0.1 g by wet weight are thus obtained.

-   -   Step 3: Basic treatment of the press cake

90.06±0.05 g press cake obtained in step 2 (Dry Matter=48±1%) and 1.80±0.02 L aqueous sodium hydroxide solution with a concentration equal to 1 mol·L⁻¹ are placed in a 2-L three-neck flask equipped with a condenser and a mechanical stirrer (Heidolph® RZR1). The medium is heated with an oil bath to a temperature of 90±2° C. for 48 hours. Throughout the reaction, the reaction medium is subjected to a stirring of 280 rpm.

-   -   Step 4: Recovery of the chitin

The reaction medium obtained at the end of step 3 is then filtered (SEFAR MEDIFAB® 03-60/42 filter) so as to recover the chitin.

-   -   Step 5: Washing of the chitin

The chitin recovered at the end of step 4 is then rinsed with tepid tap water until neutralization of the pH.

-   -   Step 6: Drying of the chitin

The chitin is then dried for 24 hours, at 60° C., in a drying oven (Binder®, FP53 model).

8.1±0.7 g chitin is thus obtained.

II. Results

The analysis methods are identical to those described in Example 1.

The properties of the thus-obtained chitin are given in Table 5 below.

TABLE 5 Properties of the chitin obtained in Example 3 Ash (g/100 g DM*) 1.825 +/− 0.40 Fats (g/100 g DM*)    0 +/− 0.00 Total aa** content (g/100 g DM*) 1.105 +/− 0.18 Molecular mass (kg · mol⁻¹)  799.5 +/− 53.03 *DM: dry matter **aa: amino acids

The relative abundance of amino acids in the chitin obtained is given in Table 6 below. It is expressed in %.

TABLE 6 Relative abundance of amino acids in the chitin obtained in Example 3 Threonine (Thr) 0.00 Serine (Ser) 0.00 Proline (Pro) 0.00 Glycine (Gly) 0.00 Glutamic acid (Glu) 0.00 Alanine (Ala) 26.56 Cysteine (Cys) 4.96 Valine (Val) 13.95 Methionine (Met) 0.00 Isoleucine (Ile) 0.00 Aspartic acid (Asp) 0.00 Leucine (Leu) 0.00 Tyrosine (Tyr) 0.00 Phenylalanine (Phe) 0.00 Histidine (His) 38.71 Lysine (Lys) 15.30 Arginine (Arg) 0.00 Tryptophan (Trp) 0.52 Total 100.00

5 amino acids appear to be particularly resistant to the method, namely alanine, cysteine, valine, histidine and lysine. Histidine, lysine and alanine are the 3 most resistant amino acids. The respective relative abundances of alanine and of valine are clearly greater than those calculated in Example 1.

Example 4: Obtaining Chitin According to the Invention from Different Insects

Different insects were used in this example: Tenebrio molitor, Pachnoda marginata, Zophobas mono and Galleria mellonella.

The cuticles were obtained from the larval stage of the different insects according to steps 1 and 2 described in Example 1.

The cuticles are then subjected to the following basic treatment: m₁ g wet cuticles obtained in the preceding step (Dry Matter=n₁%) and 1.80±0.02 L aqueous sodium hydroxide (or potassium hydroxide) solution with a concentration equal to 1.0 mol·L⁻¹ are placed in a 2-L three-neck flask equipped with a condenser and a stirrer (Heidolph® RZR1). The medium is heated with an oil bath to a temperature of 90±2° C. for 48 hours (24 h for G. mellonella). Throughout the reaction, the reaction medium is subjected to a stirring of 300 rpm. Approximately 0.05 L aqueous sodium hydroxide (or potassium hydroxide) solution per gram of dry matter of solid residue is therefore used.

After this basic treatment, steps 4 to 6 of the method from Example 1 are then performed (for P. marginata step 5 is performed with distilled water).

The experimental conditions are summarized in Table 7, in particular the ratio of base:cuticles:water is a ratio by dry weight in g for the base and the cuticles, and by weight in g for the water.

TABLE 7 Experimental conditions of the basic treatment of different insects Mass m′₁ Initial of dry Ratio of mass m₁ of n₁ % dry cuticles base:cuti- Insect Base cuticles (g) matter (g) cles:water T. molitor NaOH 90.03 ± 0.02 40.06 ± 0.00 36.06 ± 0.01   2:1:50 T. molitor KOH 90.33 ± 0.18 41.23 ± 1.63 37.24 ± 1.44 2.7:1:48 P. marginata NaOH 110.62 ± 0.58  31.58 ± 1.24 34.93 ± 1.55 2.1:1:51 Z. morio NaOH 75.11 ± 0.07 45.29 ± 1.63 34.02 ± 1.24 2.1:1:53 G. mellonella NaOH 100.63 ± 0.56  34.44 ± 1.40 34.65 ± 1.40 2.1:1:52

A mass m₂ of chitin is finally collected. The yield is calculated as follows: m₂/m′₁*100 and the results are indicated in Table 8.

TABLE 8 Chitin extraction yields for different insects Mass m₂ of Insect chitin obtained (g) Yield (%) T. molitor 6.28 ± 0.19 17.4 ± 0.5 T. molitor 8.12 ± 0.32 21.8 ± 1.3 P. marginata 7.95 ± 0.24 22.8 ± 1.2 Z. morio 5.93 ± 0.78 17.4 ± 2.2 G. mellonella 7.05 ± 0.54 20.4 ± 1.5

The chitins are then analyzed according to the analysis methods indicated in point II of Example 1. The analysis results are given in Table 9, in which the ash, lipid and amino acid contents correspond to contents in grams per 100 g dry matter.

TABLE 9 Properties of the chitins obtained from different insects Molar Purity by Source of mass Amino difference chitin (kDa) Ash Lipids acids (%) T. molitor 1015 ± 98  1.71 ± 0.11   0 ± 0.00 0.68 ± 0.03 97.61 ± 0.12 (NaOH) T. molitor 886 ± 49 2.58 ± 0.04 0.71 ± 0.40 0.32 ± 0.01 96.39 ± 0.40 (KOH) P. 1932 ± 66  2.56 ± 0.13 0.33 ± 0.25 0.25 ± 0.07 96.86 ± 0.29 marginata Z. morio 865 ± 51 1.57 ± 0.00 0.32 ± 0.01 0.535 ± 0.19  97.575 ± 0.19  G. 1626 ± 107 1.635 ± 0.06    0 ± 0.00 0.18 ± 0.06 98.185 ± 0.19  mellonella

The method according to the invention makes it possible to obtain a chitin with a high molecular mass, also having a high purity, whatever the insect or basic treatment used.

The relative abundance of amino acids in the chitins obtained is given in Table 10 below and is expressed in percent.

TABLE 10 Relative abundance of amino acids in the chitins obtained from different insects T. molitor T. molitor (NaOH) (KOH) P. marginata Z. morio G. mellonella threonine 0.000 0.000 31.955 38.261 0.000 serine 0.000 0.000 0.000 0.000 0.000 proline 0.000 0.000 0.000 0.000 0.000 glycine 0.000 0.000 0.000 0.000 0.000 glutamic acid 0.000 0.000 0.000 3.733 0.000 alanine 12.476 24.845 0.000 23.330 0.000 cysteine 5.871 0.000 0.000 0.000 0.000 valine 8.073 0.000 0.000 23.330 0.000 methionine 0.000 0.000 0.000 0.000 0.000 isoleucine 0.000 0.000 0.000 0.000 0.000 aspartic acid 0.000 0.000 0.000 0.000 0.000 leucine 0.000 0.000 0.000 0.000 0.000 tyrosine 0.000 0.000 0.000 11.198 0.000 phenylalanine 0.000 0.000 0.000 0.000 0.000 histidine 44.767 0.000 0.000 0.000 0.000 lysine 28.622 74.534 67.905 0.000 99.174 arginine 0.000 0.000 0.000 0.000 0.000 tryptophan 0.191 0.621 0.140 0.149 0.826 total 100.000 100.000 100.000 100.000 100.000

The conditions of the basic treatment (NaOH or KOH) as well as the insects used influence the amino acid composition of the resulting chitin.

Example 5: Obtaining Chitosan According to the Invention from Different Insects

-   -   Grinding of the chitin

Each chitin obtained in Example 4 is finely ground in a centrifugal grinder (Retsch® ZM200) with a strainer with pores of 250 μm.

-   -   Deacetylation of the chitin

A mass of m₃ g of the chitin obtained after the grinding step and a volume V₁ (V₁=m₃*50 mL) of aqueous sodium hydroxide (or potassium hydroxide) solution with a concentration equal to 19 mol·L⁻¹ are placed in a 2-L three-neck flask equipped with a condenser and a stirrer (Heidolph® RZR1). The medium is heated with an oil bath to a temperature of 100±2° C. for 2 hours. Throughout the reaction, the reaction medium is subjected to a stirring of 300 rpm.

-   -   Recovery of the chitosan

The reaction medium obtained at the end of the deacetylation step is then filtered (SEFAR MEDIFAB® 03-60/42 filter) so as to recover the chitosan.

-   -   Washing of the chitosan

The chitosan recovered is then rinsed with tepid tap water until neutralization of the pH.

It is then made to react again in a three-neck flask containing the same quantity of aqueous sodium hydroxide (or potassium hydroxide) solution and the 3 preceding steps (deacetylation, recovery and washing) are repeated identically.

-   -   Drying of the chitosan

The steps of deacetylation, recovery and washing are therefore carried out twice in total. At the end of these steps, the chitosan is dried for 24 hours, at 60° C., in a drying oven (Binder®, FP53 model). A mass ma of chitosan is collected. The yield is calculated as follows: m₄/m₃*100 and the results are summarized in Table 11. In particular, Table 11 refers to the ratio of base:chitin:water, which is a ratio by dry weight in g for the base and the chitin, and by weight in g for the water.

TABLE 11 Masses of chitin, volume of base and yield for obtaining chitosan depending on the insects Volume Mass m₄ of Initial V₁ of Ratio of chitosan Source of mass m₃ of base used base:chi- obtained chitin Base chitin (g) (mL) tin:water (g) Yield (%) T. molitor NaOH 12.02 ± 0.24 601 ± 12 38:1:50 8.83 ± 0.25 73.4 ± 0.6 (NaOH) T. molitor KOH 13.73 ± 0.49 686 ± 24 53:1:50 9.17 ± 0.27 66.9 ± 4.3 (KOH) P. NaOH 16.78 ± 3.51  839 ± 175 38:1:50 11.11 ± 2.52  66.1 ± 1.2 marginata Z. morio NaOH 13.91 ± 0.28 696 ± 14 38:1:50 9.61 ± 0.09 69.1 ± 2.1 G. NaOH 16.80 ± 0.01 840 ± 0  38:1:50 11.19 ± 0.60  66.6 ± 3.6 mellonella

The chitosans are then analyzed according to the analysis methods indicated in point II of Example 1. The analysis results are given in Table 12, in which the ash, lipid and amino acid contents correspond to contents in grams per 100 g dry matter. In this table, the lipid content measured is at the detection limit.

TABLE 12 Properties of the chitosans obtained from different insects Molar Purity by Source of mass Amino difference chitosan (kDa) Ash Lipids acids (%) T. molitor 379 ± 31 2.305 ± 0.29  0.455 ± 0.01 0.245 ± 0.08 96.995 ± 0.30  (NaOH) T. molitor 593 ± 9  1.81 ± 0.11 0.245 ± 0.01 0.375 ± 0.01 97.57 ± 0.11 (KOH) P. 561 ± 74 2.71 ± 0.03 0.385 ± 0.05 0.215 ± 0.01 96.69 ± 0.06 marginata Z. morio 430 ± 11 1.24 ± 0.16  0.53 ± 0.01  0.26 ± 0.06 97.97 ± 0.17 G. 483 ± 29 0.99 ± 0.04 0.665 ± 0.02 0.265 ± 0.01 98.08 ± 0.05 mellonella

As the method according to the invention makes it possible to obtain a chitin with a high molecular mass and purity, the resulting chitosan also has these features, even under different deacetylation conditions. 

The invention claimed is:
 1. Chitin isolated or extracted from insects, having (a) a molecular mass greater than or equal to 855 kg.mol⁻¹ and containing less than 1.5% by weight amino acids relative to the total dry weight of chitin, wherein the molecular mass is determined using the falling ball viscosity measurement; and (b) purity by difference greater than or equal to 95%, wherein the purity by difference is obtained by subtracting the amino acid, lipid and ash impurity contents from the absolute purity value, said absolute purity value being equal to 100%.
 2. Chitin according to claim 1, containing less than 3% by weight ash relative to the total dry weight of chitin.
 3. Chitosan obtained from chitin isolated or extracted from insects, having a molecular mass greater than or equal to 250 kg.mol⁻¹ and a purity by difference greater than or equal to 95%, wherein the molecular mass is determined using the falling ball viscosity measurement and wherein the purity by difference is obtained by subtraction of the amino acid, lipid, and ash impurity contents from the absolute purity value, said absolute purity value being equal to 100%.
 4. Method for obtaining chitin and/or chitosan, from insects, comprising the following steps: (i.) separation of the cuticles from the soft part of the insects, then (ii.) basic treatment of the cuticles obtained at step (i) for a duration comprised between 5 and 60 hours with an aqueous basic solution, wherein the molar concentration of the base in aqueous solution is comprised between 0.1 and 5 mol.L⁻¹, (iii.) recovery of the chitin from step (ii), (iv.) optionally, deacetylation of the chitin to produce chitosan, wherein no step of grinding the insects is performed prior to the step of separating the cuticles from the soft part and wherein no step of said method is carried out at a pH lower than
 6. 5. Method according to claim 4, in which the separation of the cuticles from the soft part of the insects is performed using a belt separator.
 6. Method according to claim 4, in which the separation of the cuticles from the soft part of the insects is performed using a filter press.
 7. Method according to claim 4, in which the basic treatment is carried out with a strong base.
 8. Method according to claim 4, in which the basic treatment is carried out at a temperature comprised between 60 and 100° C.
 9. Method for obtaining chitin, from insects, comprising the following steps: (i.) killing of the insects, (ii.) separation of the cuticles from the soft part of the insects, (iii.) basic treatment of the cuticles obtained at step (ii) for a duration comprised between 5 and 60 hours with an aqueous basic solution, wherein the molar concentration of the base in aqueous solution is comprised between 0.1 and 5 mol.L⁻¹, (iv.) recovery of the chitin from step (iii), wherein no step of grinding the insects is performed prior to the step of separating the cuticles from the soft part and wherein no step of said method is carried out at a pH lower than
 6. 10. Chitin obtained from the method according to claim 4, wherein said chitin has a purity by difference greater than or equal to 95%, wherein the purity by difference is obtained by subtracting the amino acid, lipid and ash impurity contents from the absolute purity value, said absolute purity value being equal to 100%.
 11. Method for obtaining chitosan, from insects, comprising the following steps: (i.) killing of the insects, (ii.) separation of the cuticles from the soft part of the insects, (iii.) basic treatment of the cuticles obtained at step (ii) for a duration comprised between 5 and 60 hours with an aqueous basic solution, wherein the molar concentration of the base in aqueous solution is comprised between 0.1 and 5 mol.L⁻¹, (iv.) recovery of the chitin from step (iii), (v.) deacetylation of the chitin, and (vi.) recovery of the chitosan, wherein no step of grinding the insects is performed prior to the step of separating the cuticles from the soft part and wherein no step of said method is carried out at a pH lower than
 6. 12. Chitosan obtained from the method according to claim 4, wherein said chitin recovered in step iii has a purity by difference greater than or equal to 95%, wherein the purity by difference is obtained by subtracting the amino acid, lipid and ash impurity contents from the absolute purity value, said absolute purity value being equal to 100%.
 13. Chitosan obtained from the method according to claim 11, wherein said chitin recovered in step iv has a purity by difference greater than or equal to 95%, wherein the purity by difference is obtained by subtracting the amino acid, lipid and ash impurity contents from the absolute purity value, said absolute purity value being equal to 100%. 